In the understanding/conformance.html document, there is an empty link <a href="#accessibility-support-documenting"> in the 'documented-lists' section
<p>Authors, companies or others may wish to create and use their own compilations of
accessibility-supported technology uses and this is allowed in meeting WCAG. Customers,
companies or others may, however, specify that technology uses from a custom or public
compilation be used. See
<a href="#accessibility-support-documenting"></a>.
</p>